The pressure in the equation should be the difference between suction and discharge pressure in Pa units.
Though your system is recirculating your system will have some friction pressure loss, that the pump has got to give.
Heare you can see grundfos literature about a pump with an integrated VFD:
http://net.grundfos.com/Appl/WebCAPS/litctrl?cmd=com.grundfos.webcaps.literature.commands.LiteratureDetail&documentid=234313&litlanguage=ENU&typecode=NBE00&appcode=AIRCON&pdfid=2667276#
Page 24, figure 33, min. curve...
If the system with high static pressure, it can be posible, that running at 20Hz means you have no flow. That's not the case with system with no static pressure, so the two situations are completlly different.
cholopa
Danfoss makes VFD's not pumps.
VFD´s has no problem running at low Hz's.
Pump manufacters also say that minimum Hz's for a VFD pump is around 20 HZ.
But for me, the point is that a pump running in a loop with no static pressure has to make a much less effort than a pump running in a loop with...
I have realice that the graph i've point out, is for "fixed" r.p.m, wich is not the case when using VFD's.
What happens to that graph when reducing r.p.m's?. The effects can be seen in the same report, figure 12. In one hand, you can see that reducing r.p.m's reduces the efficency, but on the...
Thanks for your welcomes and replays.
Let me put this in perspective. I will change the numbers so it makes more sense (sorry i'm not used to use I-P units).
For keeping and industrial place at comfortable temperature (72 ºF), an AHU has got a water coil that works at a AT of 10ºF (44-54 ºF...
Hi:
I've been searching on this topic a lot and i can't find a reason why a pump can't operate at 1 Hz in the following conitions:
A system in a big AHU(cooling coil) with one VFD pump and no three way or two way valves.
Let's say at a given point a need 10% of the cooling power of that ahu...
